1. Field of the Invention
The present invention relates to brushless direct current (D.C.) motors with a smaller thickness.
2. Description of the Related Art
FIGS. 1 and 2 illustrate a conventional brushless motor that acts as a heat-dissipating fan. Heat-dissipating fans are widely used for electric elements and central processors that generate heat when operating. In order to be utilized in a limited space, it is a trend to minimize the thickness and volume of the fans so as to provide wider applications.
As illustrated in FIGS. 1 and 2, the conventional D.C. motor type heat-dissipating fan 9 includes a housing 91 with an axle tube 92 mounted thereto. A stator bobbin 93 and a circuit board 96 are mounted around the axle tube 92. The stator bobbin has been wound with coils and includes an upper polar plate 94 and lower polar plate 95. A shaft 98 of a rotor 97 is rotatably held by the axle tube 92. Such a D.C. motor type heat-dissipating fan 9 has a certain thickness. It is, therefore, relatively difficult for manufacturers to reduce the thickness of the D.C. motor heat-dissipating fan with currently necessary members.
In the conventional D.C. motor type heat-dissipating fan 9, the circuit board 96 includes at least a Hall sensor and a drive circuit, wherein the drive circuit consists of at least two transistors and necessary electronic elements. The Hall sensor is used to detect the polarity of the ring magnet of the rotor, and the rotor is driven by the drive circuit to turn. Thus, the elements on the circuit board 96 are not omittable in conventional D.C. motor type heat dissipating fans. Nevertheless, it would be of great help in reducing the thickness of the motors if the space occupied by the circuit board could be reduced without adversely affecting the functions of the motors.
It is the primary object of the present invention to provide an improved brushless D.C. motor structure with minimized volume and thickness by reducing elements on the circuit board while maintaining original functions of the brushless D.C. motor.
It is another object of the present invention to provide an improved brushless D.C. motor structure that can be easily manufactured and assembled by reducing elements on the circuit board while maintaining original functions of the brushless D.C. motor.
A brushless D.C. motor in accordance with the present invention comprises a stator, a rotor, and a drive means. An axle tube is extended through the stator and includes a bearing mounted therein for rotatably holding a shaft of the rotor. The drive means detects polarity of a ring magnet of the rotor and drives the rotor to turn. The drive means is fixed to a stator bobbin or fixed at a position below the ring magnet.
Other objects, specific advantages, and novel features of the invention will become more apparent from the following detailed description and preferable embodiments when taken in conjunction with the accompanying drawings.